Detectability of an AMOC decline in current and projected climate changes

Determining whether the Atlantic Meridional Overturning Circulation (AMOC)'s transport is in decline is challenging due to the short duration of continuous observations. To estimate how many years are needed to detect a decline, we conduct a simulation study using synthetic data that mimics an AMOC time series. The time series' characteristics are reproduced using the trend, variance, and autocorrelation coefficient of the AMOC strength at 26.5°N from 20 Coupled Model Intercomparison Project Phase 5 (CMIP5) models under the RCP8.5 future scenario, and from RAPID observations (2004–2018). Our results suggest that the 14‐year RAPID length has just entered the lower limits of the trend's “detection window” based on synthetic data generated using CMIP5 trends and variability (14–42 years; median urn:x-wiley:grl:media:grl61393:grl61393-math-0001 24 years), but twice the length is required for detectability based on RAPID variability (29–67 years; median urn:x-wiley:grl:media:grl61393:grl61393-math-0002 43 years). The annual RAPID trend is currently not statistically significant (−0.11 Sv yr−1, p > 0.05).